You can see its very tight. I was able to make a single-DIN panel for 4 gauges two switches and room left for some status LEDs and maybe a momentary switch or two. Above you see I've installed two gauges in the Pod; not where I want them but it was free space.

They are very nice instruments with a relay output and configurable relay trigger. I've been able to create a rudimentary control logic with these are automotive relays to switch the loads:

Note: WVO means the secondary fuel system, COMMON is the injector pump. We have to isolate the WVO from the regular diesel tank. WVO is not safe to leave in the fuel system when the engine is not running.

When the main fuel select switch is ON and the Temp and Pressure are compliant, the Supply and Return valves as well as the fuel pump are activated. When the mail switch is set to PURGE, the Return valve alone is activated. So basically my relays are set up in series like gates.

Why I want to change to a microcontroller based system:

The WVO control circuit above is a very crude design, and it lacks some necessary improvements. I have two electric heaters I want to control like a thermostat, and I want to enable the ability to auto-purge the system with a timer (its possible now to forget about PURGE and overfill the WVO tank). Additionally auto-purge can run after the key is removed from the ignition, much like a turbo timer which is common on diesel trucks. Right now we do this by shorting pins on the remote starter, but a relay to control the ignition circuit is another solution (my vehicle is older, has a simple ignition circuit). Ultimately I want a smart timer that is aware of the ignition state and will run the auto-purge cycle (e.g. 5 mins) even if it started before the vehicle was parked.

Also I want to add some more sensors (a lot more) and potentially perform some data logging.

There are some boxed solutions that do almost all of this but they are closed and do not provide for hacking. Nothing to be learned from these.

So this project is my educational opportunity. I was going to tackle this from scratch but the work done here is so nice and open source that I think its worth the time investment to learn it and test, ultimately contributing to the project. Because a lot of people are running WVO it could add attention to the project and help increase the profile.

you can attach 4 buttons to the V2 directly, where 3 from that will cover your fuel switch

Temp and fuel sensors should work also, the Inputs are made for VDO sensor, but they basically measure resistance.
Maybe you will need to measure your sensors and correct the lookup tables, we will help you on that

For the 4 relays you will need either transistors or i would prefer using a ULN2003 Driver.
That will give you 7 outputs with enough power to drive relays, and does not need a lot of space.